Effects of Prosopis velutina Invasion on Soil Characteristics along the Riverine System of the Molopo River in North-West Province, South Africa

Abstract

Invasive alien plants are one of the major threats to ecosystems. Many invasive plant species, such as Prosopis species, have been introduced around the world and can alter the soil properties of invaded ecosystems. It is one of the most aggressive invasive plant invaders in the North-West Province of South Africa, but little information is available about their influence on soil properties. This study was conducted to investigate the effect of Prosopis velutina invasion on selected soil properties at five different sites along the riverine system of the Molopo River in North West Province. At each study site, soil characteristics were measured from soil samples taken under P. velutina canopies, between canopies and in the benchmark stands free of Prosopis species. The effect on selected soil properties of P. velutina invasion varied between the three stands and between sites. In all the sites, almost all soils collected from under the canopies had a significantly higher soil exchangeable Ca, K, Mg, and Na, organic matter (OM), total nitrogen (TN), available phosphorus (P), Electrical conductivity (EC), and cation exchange capacity (CEC) than the other sample positions, except for the pH which had the high value in intercanopies. Significantly higher (p<0.05) values of almost all soil properties were found on the densely invaded sites (Tshidilamolomo I and Tshidilamolomo II) compared to lightly invaded sites (Mabule, Black Heat Farm, and Bray). However, it was difficult to generalise as the effects often appear to be site-specific. In addition, the findings also indicated that soils textural classes ranged between sand, silt, and clay in all study sites with a higher proportion of sand in the benchmark than in the soil under the canopies and intercanopies. Soil characteristics differed significantly more between sites than among positions. The site effects observed in this current study provide evidences that this species may occupy a relatively broad soil niche.